Hi Luke,
It does not seem to capture the reason for controller B reporting degraded status.
I would recommend to first fix controller B issues before replacing controller A.
Restarting storage controller B after scheduling a down time would be a good idea if its a false alert.
Share the output of the following commands:
show cache-parameters
show vdisks
show ports
Confirm whether the show network-parameters output indicates health status
Have you already tried restarting storage controller A and removing/reseating it?
It would be good if you can engage HPE support team through chat option to review the logs and provide the recommendations. I believe that basic support would be available even for out of warranty units.
https://support.hpe.com/hpesc/home/chat